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<a name="1" href="#1">1</a>   <em class="jxr_javadoccomment">/**</em>
<a name="2" href="#2">2</a>   <em class="jxr_javadoccomment"> * Copyright (c) 2009 Cerner Corporation.</em>
<a name="3" href="#3">3</a>   <em class="jxr_javadoccomment"> * All rights reserved. This program and the accompanying materials</em>
<a name="4" href="#4">4</a>   <em class="jxr_javadoccomment"> * are made available under the terms of the Eclipse Public License v1.0</em>
<a name="5" href="#5">5</a>   <em class="jxr_javadoccomment"> * which accompanies this distribution, and is available at</em>
<a name="6" href="#6">6</a>   <em class="jxr_javadoccomment"> * <a href="http://www.eclipse.org/legal/epl-v10.html" target="alexandria_uri">http://www.eclipse.org/legal/epl-v10.html</a></em>
<a name="7" href="#7">7</a>   <em class="jxr_javadoccomment"> *</em>
<a name="8" href="#8">8</a>   <em class="jxr_javadoccomment"> * Contributors:</em>
<a name="9" href="#9">9</a>   <em class="jxr_javadoccomment"> *    Cerner Corporation - initial API and implementation</em>
<a name="10" href="#10">10</a>  <em class="jxr_javadoccomment"> */</em>
<a name="11" href="#11">11</a>  <strong class="jxr_keyword">package</strong> com.cerner.system.<strong class="jxr_keyword">rest</strong>.retry;
<a name="12" href="#12">12</a>  
<a name="13" href="#13">13</a>  <strong class="jxr_keyword">import</strong> java.util.concurrent.Callable;
<a name="14" href="#14">14</a>  <strong class="jxr_keyword">import</strong> java.util.concurrent.locks.Lock;
<a name="15" href="#15">15</a>  <strong class="jxr_keyword">import</strong> java.util.concurrent.locks.ReadWriteLock;
<a name="16" href="#16">16</a>  <strong class="jxr_keyword">import</strong> java.util.concurrent.locks.ReentrantReadWriteLock;
<a name="17" href="#17">17</a>  <strong class="jxr_keyword">import</strong> java.util.logging.Level;
<a name="18" href="#18">18</a>  
<a name="19" href="#19">19</a>  <strong class="jxr_keyword">import</strong> com.cerner.system.<strong class="jxr_keyword">rest</strong>.internal.arguments.NotNulls;
<a name="20" href="#20">20</a>  
<a name="21" href="#21">21</a>  <em class="jxr_javadoccomment">/**</em>
<a name="22" href="#22">22</a>  <em class="jxr_javadoccomment"> * API to recover from failures. The implementation supports concurrent failures</em>
<a name="23" href="#23">23</a>  <em class="jxr_javadoccomment"> * without causing interference of the retry logic. The usefulness of fault</em>
<a name="24" href="#24">24</a>  <em class="jxr_javadoccomment"> * barriers is best understood by comparing and contrasting &lt;a href="<a href="http://www.oracle.com/technology/pub/articles/dev2arch/2006/11/effective-exceptions2.html" target="alexandria_uri">http://www.oracle.com/technology/pub/articles/dev2arch/2006/11/effective-exceptions2.html</a>"</em>
<a name="25" href="#25">25</a>  <em class="jxr_javadoccomment"> * &gt;faults and contingencies&lt;/a&gt;.</em>
<a name="26" href="#26">26</a>  <em class="jxr_javadoccomment"> * </em>
<a name="27" href="#27">27</a>  <em class="jxr_javadoccomment"> * @author Alex Horn</em>
<a name="28" href="#28">28</a>  <em class="jxr_javadoccomment"> * @author David Edwards</em>
<a name="29" href="#29">29</a>  <em class="jxr_javadoccomment"> */</em>
<a name="30" href="#30">30</a>  <strong class="jxr_keyword">public</strong> <strong class="jxr_keyword">class</strong> <a href="../../../../../com/cerner/system/rest/retry/FaultBarrier.html">FaultBarrier</a> {
<a name="31" href="#31">31</a>  
<a name="32" href="#32">32</a>    <em class="jxr_javadoccomment">/**</em>
<a name="33" href="#33">33</a>  <em class="jxr_javadoccomment">   * Log failures as well as fatal errors from which the retry logic was not</em>
<a name="34" href="#34">34</a>  <em class="jxr_javadoccomment">   * able to recover.</em>
<a name="35" href="#35">35</a>  <em class="jxr_javadoccomment">   */</em>
<a name="36" href="#36">36</a>    <strong class="jxr_keyword">private</strong> <strong class="jxr_keyword">final</strong> <a href="../../../../../com/cerner/system/rest/retry/FaultBarrierLogger.html">FaultBarrierLogger</a> logger;
<a name="37" href="#37">37</a>  
<a name="38" href="#38">38</a>    <em class="jxr_javadoccomment">/**</em>
<a name="39" href="#39">39</a>  <em class="jxr_javadoccomment">   * The read lock should be held for normal operation and the write lock must</em>
<a name="40" href="#40">40</a>  <em class="jxr_javadoccomment">   * be acquired when the retry logic is invoked in order to eliminate</em>
<a name="41" href="#41">41</a>  <em class="jxr_javadoccomment">   * interference of concurrent operations.</em>
<a name="42" href="#42">42</a>  <em class="jxr_javadoccomment">   */</em>
<a name="43" href="#43">43</a>    <strong class="jxr_keyword">private</strong> <strong class="jxr_keyword">final</strong> ReadWriteLock lock;
<a name="44" href="#44">44</a>  
<a name="45" href="#45">45</a>    <em class="jxr_javadoccomment">/**</em>
<a name="46" href="#46">46</a>  <em class="jxr_javadoccomment">   * Guard against multiple retry attempts. Use the {@link #lock} to protect</em>
<a name="47" href="#47">47</a>  <em class="jxr_javadoccomment">   * access to this integer field.</em>
<a name="48" href="#48">48</a>  <em class="jxr_javadoccomment">   * &lt;p&gt;</em>
<a name="49" href="#49">49</a>  <em class="jxr_javadoccomment">   * It acts as a ticket dispatcher where a thread only initiates the retry</em>
<a name="50" href="#50">50</a>  <em class="jxr_javadoccomment">   * logic if its local ticket number is the same to the global value.</em>
<a name="51" href="#51">51</a>  <em class="jxr_javadoccomment">   */</em>
<a name="52" href="#52">52</a>    <strong class="jxr_keyword">private</strong> <strong class="jxr_keyword">int</strong> retry = 0;
<a name="53" href="#53">53</a>  
<a name="54" href="#54">54</a>    <em class="jxr_javadoccomment">/**</em>
<a name="55" href="#55">55</a>  <em class="jxr_javadoccomment">   * Internal constructor to inject a lock to eliminate interleaving of retry</em>
<a name="56" href="#56">56</a>  <em class="jxr_javadoccomment">   * operations as well as a custom logger. Subclasses must synchronize against</em>
<a name="57" href="#57">57</a>  <em class="jxr_javadoccomment">   * the injected lock when calling the logger.</em>
<a name="58" href="#58">58</a>  <em class="jxr_javadoccomment">   */</em>
<a name="59" href="#59">59</a>    <strong class="jxr_keyword">protected</strong> <a href="../../../../../com/cerner/system/rest/retry/FaultBarrier.html">FaultBarrier</a>(<strong class="jxr_keyword">final</strong> ReadWriteLock lock,
<a name="60" href="#60">60</a>        <strong class="jxr_keyword">final</strong> <a href="../../../../../com/cerner/system/rest/retry/FaultBarrierLogger.html">FaultBarrierLogger</a> logger) {
<a name="61" href="#61">61</a>      <strong class="jxr_keyword">this</strong>.logger = logger;
<a name="62" href="#62">62</a>      <strong class="jxr_keyword">this</strong>.lock = lock;
<a name="63" href="#63">63</a>    }
<a name="64" href="#64">64</a>  
<a name="65" href="#65">65</a>    <em class="jxr_javadoccomment">/**</em>
<a name="66" href="#66">66</a>  <em class="jxr_javadoccomment">   * Convenience constructor for an object that is able to orchestrate the</em>
<a name="67" href="#67">67</a>  <em class="jxr_javadoccomment">   * recovery of exceptions. Abnormal execution flows are reported to the JDK</em>
<a name="68" href="#68">68</a>  <em class="jxr_javadoccomment">   * logger in form of {@link Level#INFO} messages.</em>
<a name="69" href="#69">69</a>  <em class="jxr_javadoccomment">   */</em>
<a name="70" href="#70">70</a>    <strong class="jxr_keyword">public</strong> <a href="../../../../../com/cerner/system/rest/retry/FaultBarrier.html">FaultBarrier</a>() {
<a name="71" href="#71">71</a>      <strong class="jxr_keyword">this</strong>(JdkFaultBarrierLogger.create(Level.INFO));
<a name="72" href="#72">72</a>    }
<a name="73" href="#73">73</a>  
<a name="74" href="#74">74</a>    <em class="jxr_javadoccomment">/**</em>
<a name="75" href="#75">75</a>  <em class="jxr_javadoccomment">   * Constructor for an object that is able to orchestrate the recovery of</em>
<a name="76" href="#76">76</a>  <em class="jxr_javadoccomment">   * exceptions.</em>
<a name="77" href="#77">77</a>  <em class="jxr_javadoccomment">   */</em>
<a name="78" href="#78">78</a>    <strong class="jxr_keyword">public</strong> <a href="../../../../../com/cerner/system/rest/retry/FaultBarrier.html">FaultBarrier</a>(<strong class="jxr_keyword">final</strong> <a href="../../../../../com/cerner/system/rest/retry/FaultBarrierLogger.html">FaultBarrierLogger</a> logger) {
<a name="79" href="#79">79</a>      <strong class="jxr_keyword">this</strong>(<strong class="jxr_keyword">new</strong> ReentrantReadWriteLock(), logger);
<a name="80" href="#80">80</a>    }
<a name="81" href="#81">81</a>  
<a name="82" href="#82">82</a>    <em class="jxr_javadoccomment">/**</em>
<a name="83" href="#83">83</a>  <em class="jxr_javadoccomment">   * Same as {@link #execute(Callable, RetryHandler)} with a retry handler that</em>
<a name="84" href="#84">84</a>  <em class="jxr_javadoccomment">   * is {@code null}.</em>
<a name="85" href="#85">85</a>  <em class="jxr_javadoccomment">   */</em>
<a name="86" href="#86">86</a>    <strong class="jxr_keyword">public</strong> <strong class="jxr_keyword">final</strong> &lt;S&gt; S execute(<strong class="jxr_keyword">final</strong> Callable&lt;S&gt; callable) <strong class="jxr_keyword">throws</strong> Exception {
<a name="87" href="#87">87</a>      <strong class="jxr_keyword">return</strong> execute(callable, <strong class="jxr_keyword">null</strong>);
<a name="88" href="#88">88</a>    }
<a name="89" href="#89">89</a>  
<a name="90" href="#90">90</a>    <em class="jxr_javadoccomment">/**</em>
<a name="91" href="#91">91</a>  <em class="jxr_javadoccomment">   * Delegate to {@link Callable#call()} but handle any exceptions that it may</em>
<a name="92" href="#92">92</a>  <em class="jxr_javadoccomment">   * throw. If in fact a fault occurs, then the</em>
<a name="93" href="#93">93</a>  <em class="jxr_javadoccomment">   * {@link RetryHandler#retry(Callable, Exception)} logic will be invoked</em>
<a name="94" href="#94">94</a>  <em class="jxr_javadoccomment">   * provided that the {@code retryHandler} is not {@code null}. If the retry</em>
<a name="95" href="#95">95</a>  <em class="jxr_javadoccomment">   * handler is {@code null} then the callable should be invoked again but a</em>
<a name="96" href="#96">96</a>  <em class="jxr_javadoccomment">   * subclass may provide an alternative recovery strategy by overriding {@code</em>
<a name="97" href="#97">97</a>  <em class="jxr_javadoccomment">   * retry(Callable, Exception)}. Note, {@link #execute(Callable, RetryHandler)}</em>
<a name="98" href="#98">98</a>  <em class="jxr_javadoccomment">   * throws only an exception if a severe, fatal error occurs from which it</em>
<a name="99" href="#99">99</a>  <em class="jxr_javadoccomment">   * cannot recover.</em>
<a name="100" href="#100">100</a> <em class="jxr_javadoccomment">   * </em>
<a name="101" href="#101">101</a> <em class="jxr_javadoccomment">   * @param callable closure-style object that is triggered for every normal</em>
<a name="102" href="#102">102</a> <em class="jxr_javadoccomment">   *          execution flow</em>
<a name="103" href="#103">103</a> <em class="jxr_javadoccomment">   * @param retryHandler closure-style object whose</em>
<a name="104" href="#104">104</a> <em class="jxr_javadoccomment">   *          {@link RetryHandler#retry(Callable, Exception)} method is invoked</em>
<a name="105" href="#105">105</a> <em class="jxr_javadoccomment">   *          if the normal execution path results in an exception</em>
<a name="106" href="#106">106</a> <em class="jxr_javadoccomment">   * @throws Exception if the {@link RetryHandler} could not recover from the</em>
<a name="107" href="#107">107</a> <em class="jxr_javadoccomment">   *           failure</em>
<a name="108" href="#108">108</a> <em class="jxr_javadoccomment">   * @throws IllegalArgumentException if the callable is {@code null}</em>
<a name="109" href="#109">109</a> <em class="jxr_javadoccomment">   * @see RetryHandler#retry(Callable, Exception)</em>
<a name="110" href="#110">110</a> <em class="jxr_javadoccomment">   */</em>
<a name="111" href="#111">111</a>   <strong class="jxr_keyword">public</strong> <strong class="jxr_keyword">final</strong> &lt;S&gt; S execute(<strong class="jxr_keyword">final</strong> Callable&lt;S&gt; callable,
<a name="112" href="#112">112</a>       <strong class="jxr_keyword">final</strong> RetryHandler&lt;S&gt; retryHandler) <strong class="jxr_keyword">throws</strong> Exception {
<a name="113" href="#113">113</a>     NotNulls.names(<span class="jxr_string">"callable"</span>).values(callable);
<a name="114" href="#114">114</a> 
<a name="115" href="#115">115</a>     <strong class="jxr_keyword">int</strong> _retry = 0;
<a name="116" href="#116">116</a>     S exit = <strong class="jxr_keyword">null</strong>;
<a name="117" href="#117">117</a>     Exception failure = <strong class="jxr_keyword">null</strong>;
<a name="118" href="#118">118</a> 
<a name="119" href="#119">119</a>     <strong class="jxr_keyword">final</strong> Lock readLock = <strong class="jxr_keyword">this</strong>.lock.readLock();
<a name="120" href="#120">120</a>     readLock.lock();
<a name="121" href="#121">121</a>     <strong class="jxr_keyword">try</strong> {
<a name="122" href="#122">122</a> 
<a name="123" href="#123">123</a>       <em class="jxr_comment">/*<em class="jxr_comment"> copy by value with read lock held */</em></em>
<a name="124" href="#124">124</a>       _retry = <strong class="jxr_keyword">this</strong>.retry;
<a name="125" href="#125">125</a> 
<a name="126" href="#126">126</a>       exit = callable.call();
<a name="127" href="#127">127</a>     } <strong class="jxr_keyword">catch</strong> (<strong class="jxr_keyword">final</strong> Exception e) {
<a name="128" href="#128">128</a>       <em class="jxr_comment">/*<em class="jxr_comment"> INFO: encountered failure but attempt to recover */</em></em>
<a name="129" href="#129">129</a>       <strong class="jxr_keyword">this</strong>.logger.recover(e);
<a name="130" href="#130">130</a> 
<a name="131" href="#131">131</a>       failure = e;
<a name="132" href="#132">132</a>     } <strong class="jxr_keyword">finally</strong> {
<a name="133" href="#133">133</a>       readLock.unlock();
<a name="134" href="#134">134</a>     }
<a name="135" href="#135">135</a> 
<a name="136" href="#136">136</a>     <strong class="jxr_keyword">if</strong> (failure != <strong class="jxr_keyword">null</strong>) {
<a name="137" href="#137">137</a>       <strong class="jxr_keyword">final</strong> Lock writeLock = <strong class="jxr_keyword">this</strong>.lock.writeLock();
<a name="138" href="#138">138</a>       writeLock.lock();
<a name="139" href="#139">139</a>       <strong class="jxr_keyword">try</strong> {
<a name="140" href="#140">140</a> 
<a name="141" href="#141">141</a>         <em class="jxr_comment">/*<em class="jxr_comment"> counter detects concurrent failures after read lock has been released */</em></em>
<a name="142" href="#142">142</a>         <strong class="jxr_keyword">if</strong> (_retry == <strong class="jxr_keyword">this</strong>.retry) {
<a name="143" href="#143">143</a>           <strong class="jxr_keyword">try</strong> {
<a name="144" href="#144">144</a>             <strong class="jxr_keyword">if</strong> (retryHandler == <strong class="jxr_keyword">null</strong>) {
<a name="145" href="#145">145</a>               exit = retry(callable, failure);
<a name="146" href="#146">146</a>             } <strong class="jxr_keyword">else</strong> {
<a name="147" href="#147">147</a>               <em class="jxr_comment">/*<em class="jxr_comment"> No one else has initiated the retry logic yet */</em></em>
<a name="148" href="#148">148</a>               exit = retryHandler.retry(callable, failure);
<a name="149" href="#149">149</a>             }
<a name="150" href="#150">150</a>           } <strong class="jxr_keyword">finally</strong> {
<a name="151" href="#151">151</a>             <em class="jxr_comment">/*</em>
<a name="152" href="#152">152</a> <em class="jxr_comment">             * finally { ... } block causes the FaultBarrier to disallow retries</em>
<a name="153" href="#153">153</a> <em class="jxr_comment">             * for concurrently queued up operations even if a fatal error has</em>
<a name="154" href="#154">154</a> <em class="jxr_comment">             * occurred.</em>
<a name="155" href="#155">155</a> <em class="jxr_comment">             */</em>
<a name="156" href="#156">156</a>             <strong class="jxr_keyword">this</strong>.retry++;
<a name="157" href="#157">157</a>           }
<a name="158" href="#158">158</a>         }
<a name="159" href="#159">159</a>       } <strong class="jxr_keyword">catch</strong> (<strong class="jxr_keyword">final</strong> Exception fatal) {
<a name="160" href="#160">160</a>         <em class="jxr_comment">/*<em class="jxr_comment"> Log INFO or DEBUG before fatal error propagates */</em></em>
<a name="161" href="#161">161</a>         <strong class="jxr_keyword">this</strong>.logger.abort(fatal);
<a name="162" href="#162">162</a> 
<a name="163" href="#163">163</a>         <strong class="jxr_keyword">throw</strong> fatal;
<a name="164" href="#164">164</a>       } <strong class="jxr_keyword">finally</strong> {
<a name="165" href="#165">165</a>         writeLock.unlock();
<a name="166" href="#166">166</a>       }
<a name="167" href="#167">167</a>     }
<a name="168" href="#168">168</a> 
<a name="169" href="#169">169</a>     <strong class="jxr_keyword">return</strong> exit;
<a name="170" href="#170">170</a>   }
<a name="171" href="#171">171</a> 
<a name="172" href="#172">172</a>   <em class="jxr_javadoccomment">/**</em>
<a name="173" href="#173">173</a> <em class="jxr_javadoccomment">   * Protected API to trigger the normal execution flow again after a failure</em>
<a name="174" href="#174">174</a> <em class="jxr_javadoccomment">   * occurred the first time it was invoked. This method is only called if the</em>
<a name="175" href="#175">175</a> <em class="jxr_javadoccomment">   * {@link #execute(Callable, RetryHandler)} method's retry handler was {@code</em>
<a name="176" href="#176">176</a> <em class="jxr_javadoccomment">   * null}.</em>
<a name="177" href="#177">177</a> <em class="jxr_javadoccomment">   */</em>
<a name="178" href="#178">178</a>   <strong class="jxr_keyword">protected</strong> &lt;S&gt; S retry(<strong class="jxr_keyword">final</strong> Callable&lt;S&gt; callable, <strong class="jxr_keyword">final</strong> Exception failure)
<a name="179" href="#179">179</a>       <strong class="jxr_keyword">throws</strong> Exception {
<a name="180" href="#180">180</a>     <strong class="jxr_keyword">return</strong> callable.call();
<a name="181" href="#181">181</a>   }
<a name="182" href="#182">182</a> 
<a name="183" href="#183">183</a> }
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